Always obtain the lock and do the unload

We mostly care about `reload_classes_only_on_change=true`, because
that's the default... and there, we definitely need to wait for the lock
when necessary.

railties/lib/rails/application/finisher.rb

@@ -86,7 +86,7 @@ module Finisher
       # added in the hook are taken into account.
       initializer :set_clear_dependencies_hook, group: :all do
         callback = lambda do
-          ActiveSupport::Dependencies.interlock.attempt_unloading do
+          ActiveSupport::Dependencies.interlock.unloading do
             ActiveSupport::DescendantsTracker.clear
             ActiveSupport::Dependencies.clear
           end